Incremental encoder

An incremental encoder is a linear or rotary electromechanical device that has two output signals, A and B, which issue pulses when the device is moved.^[1] Together, the A and B signals indicate both the occurrence of and direction of movement. Many incremental encoders have an additional output signal, typically designated index^[2] or Z,^[3] which indicates the encoder is located at a particular reference position. Also, some encoders provide a status output (typically designated alarm)^[4] that indicates internal fault conditions such as a bearing failure or sensor malfunction.

Unlike an absolute encoder, an incremental encoder does not indicate absolute position;^{[note 1]} it only reports changes in position and the corresponding direction of movement for each change. Consequently, to determine absolute position at any particular moment, it is necessary to send the encoder signals to an incremental encoder interface, which in turn will "track" and report the encoder's absolute position.

Incremental encoders report position increments nearly instantaneously, which allows them to monitor the movements of high speed mechanisms in near real-time. Because of this, incremental encoders are commonly used in applications that require precise measurement and control of position and velocity.

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